(1) Field of the Invention
The present invention relates in general to circuit boards and connectors, and more particularly to the sequential mating of circuit boards with their respective connectors.
(2) Description of the Prior Art
In designing electrical systems, a major consideration is the packaging of circuitry on printed circuit boards. Of the many factors to be considered, one is the quantity of connectors available for forming electrical connection between circuit boards. With conventional connectors and printed circuit boards there exists a proportional relationship between the quantity of electrical connections to a circuit board and the insertion force required to mate the printed circuit board with its connector. That is, the quantity of electrical connections to a printed circuit board increases so too does the insertion force required to mate that board with its connector. Further, insertion force varies, being high initially as a circuit board engages and spreads apart its connector's spring contacts and thereafter, is subsequently greatly reduced as the connector's spring contacts slide along the circuit board's terminals while the circuit board is being fully seated within its associated connector.
Printed circuit boards requiring high insertion force are undesirable in that they require strengthened connectors and connector mounting hardware. They also require strengthening of the printed circuit board, and in many cases require the development of special card insertion and extraction hardware.
Several methods are known to combat the high insertion force problem. Of these, one is to interconnect the circuit boards not through a connector but rather through direct contact between the two circuit boards involved. Such a technique is described in U.S. Pat. No. 3,924,918, entitled "Daughter Board Contact" to Lindsay Carlton Friend, issued Dec. 9, 1975. This patent teaches electrical connection between spaced and parallel mother and daughter boards by means of terminals secured to the mother board projecting toward the daughter board. The terminals include a pivot link arm, daughter board spring contacts, and a daughter board engaging member at the free end of the link. Such an arrangement is undesirable in that it does not allow the daughter board to be mounted in a conventional card file with the usual card guides, thus obtaining the support provided therefrom.
Another technique is described in U.S. Pat. No. 3,953,096, entitled "Free Standing Mother Daughter Printed Circuit Board Contact Arrangement" to Benjamin Charles Williams, issued Apr. 27, 1976. This patent teaches free standing metal contacts mounted, in a straight line, on a first board and adapted to receive, hold, and make electrical connection with a second circuit board. This technique as well as that described above, requires the fabrication, on the mother or first board, of connector contacts to be engaged by the second or daughter board. The inclusion of contacts on boards is costly and generally undesirable.
Yet another method to combat the high insertion force problem is taught in U.S. Pat. No. 4,008,939 issued Feb. 22, 1977 to Robert John Kinkaid titled "Axially Cammed Housing for Low Insertion Force Connector," which teaches a two piece dielectric connector housing including a rotatable shaft and electrical contacts. The connector housing is provided with receptacle passage ways adapted to receive electrical terminals. Electrical contacts mounted within the connector housing are positioned so as to not contact the electrical terminals when they are inserted into the housing thereby avoiding the high insertion force problem. Once the electrical terminals are inserted within the connector housing, the shaft is rotated to bias the electrical contacts into engagement with the terminals providing electrical contact therebetween. This technique requires manufacture of mechnically complicated and expensive connectors.
A method to combat the high insertion force problem, and overcome those objections raised above is the subject of the present invention, as hereinafter described.